Type Annotations

When you declare a variable or a constant in Swift you do not need to explicitly specify what datatype it belongs to. But if you want to define datatype for a variable or a constant, you can do it using Type Annotations

Syntax (var) : var varName: DataType

Syntax (let) : let varName: DataType

In the below example, constant myInt is a variable of type Integer and myString is a constant of type String.

//
//  main.swift
//  Swift Tutorials 2014-15
//  Constants in Swift
//
//  Created by Code2care on 15/09/14.
//  Copyright (c) 2014 Code2care. All rights reserved.
//

let myInt:Int = 20
var myString:String = "Swift is easy to learn!"


println("\(myInt)")
println("\(myString)")

Output :

20
Swift is easy to learn!
Program ended with exit code: 0

In the below example, we have tried to assing myInt of type Integer a String value and myString of type String a is a Integer value, resulting to errors.

//
//  main.swift
//  Swift Tutorials 2014-15
//  Constants in Swift
//
//  Created by Code2care on 15/09/14.
//  Copyright (c) 2014 Code2care. All rights reserved.
//

let myInt:Int = "Swift is easy to learn!"
var myString:String = 20


println("\(myInt)")
println("\(myString)")

Output :

Type 'int' does not confirm to protocol error 'StringLiteralConvertible'
Type 'String' does not confirm to protocol error 'InregerLiteralConvertible'